The present invention relates to a pilot controlled membrane valve for ventilating containers, apparatus or the like, comprising a valve housing having a first valve seat between the inlet and outlet of the housing, first valve means movable between a closed position engaging the first valve seat and an open position and including a first membrane extending transversely through the housing and defining with the latter to one side of the first valve seat a valve chamber which is connected by overpressure passage means to the inlet. The valve includes further a pilot valve having a second valve seat, second valve means including a second membrane and being movable between a closed position engaging the second valve seat and an open position, a second outlet, and means biasing said second valve means to the closed position, wherein the cross section of the second valve seat and that of the second outlet is greater than the open cross-section of the overpressure passage means.
Such valves are employed when use of remote controlled valves is too expensive or for reasons of safety cannot be applied and if, on the other hand, the operating conditions of the valve make it necessary that the pressure at which the valve opens is closely adjacent to the maximum operating pressure and if, in addition, a high degree of sealing up to the region of the valve opening pressure must be provided and/or the valve, after initial opening, must be opened to the maximum extent without increasing the operating pressure.
In a known valve of the above-mentioned construction, the pilot valve is in form of a disc valve which is controlled by membranes. An essential disadvantage of such a construction is in the rather complicated construction of the pilot valve control which is therefore liable to malfunction. This disadvantage is further increased in that, in the known construction, the medium passing through the valve flows around the pilot control mechanism, which may lead to an additional disturbing of its function. This holds especially true if the medium passing through the valve may cause corrosion, soiling or forming deposits on the various elements of the pilot valve. A failure of the pilot valve will lead to a complete breakdown of the valve arrangement, which may entail considerable damage or accidents.